An elastic standing wave propagating in a cubic piezoelectric multilayer structure

along to the direction of growth

induces a standing wave of strains

which results in a standing wave of piezoelectric fields. The field will produce an ac voltage signal across the system at the frequency of the wave. The elastic waves with varying wave length will induce a series of peak voltage signals. These peak signals appear when the half wavelength is equal to 1/odd number of each layer. If the thickness of one period is less than the wavelength

no maximum peak will appear.